We can expose cycle counters on the PMU easily. To be as compatible as
possible, let's do so, but make sure we don't expose any other architectural
counters that we can not model yet.

This allows OSs to work that require PMU support.

Signed-off-by: Alexander Graf <agraf@csgraf.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20210916155404.86958-10-agraf@csgraf.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>